The invention relates to a method for monitoring the wear of the tires of a vehicle using ultra wide band or UWB pulse transmission, and to a device for monitoring wear and an on-board system capable of executing this method.
Conventionally, tires are fitted on the rims of vehicle wheels in order to improve the adhesion of the wheels to the ground traveled over, regardless of the conditions of use. In particular, a tire comprises a tread in contact with the ground. This tread is a thick rubber layer, made of natural or synthetic rubber, in which “grooves” are cut to allow the discharge of water, snow and other loose material, thereby improving adhesion and reducing effects such as aquaplaning.
Under the tread, plies of parallel metal cords—usually two plies—are crossed over one another with the use of bonding, in order to form a stiffening belt and, in particular, to resist side thrust generated during cornering.
The tire tread becomes worn over time and the grooves tend to disappear gradually, possibly causing a loss of adhesion. In order to detect critical tire wear, beyond which point it may be considered dangerous to travel, a conventional method is to implant wear indicators. These indicators take the form of colored markers incorporated into the tread. When the tread becomes worn, its thickness decreases, and the markers eventually lie flush with the outer surface of the tread. The need to replace the tire can then be ascertained by visual inspection.
This conventional form of detection is unsatisfactory: it is imprecise, it is random because it depends on the frequency of tread inspection, and, finally, it is ineffective because the critical nature of this detection is not backed up by any alarm.
Consequently, other methods have been developed to overcome these drawbacks. One method is based on the incorporation of at least one wireless tag or RFID tag (“Radio Frequency Identification”) marker in the tread of each tire, at a location corresponding to critical wear. This method is described, for example, in patent application US 2006/0042734.
In this method, the RFID tag is activated by a presence signal supplied by a transmitter, and transmits a confirmation signal to a detector in response. When the tire reaches critical wear, the tag is destroyed and ceases to respond to the presence signal: this lack of response triggers an alarm to warn the driver of the state of wear of the tire or tires.
Another method is that of associating a piezoelectric element, incorporated in the tire tread, with a generator of radio waves which are transmitted on the basis of the voltage signal generated by the piezoelectric element. Patent document EP 2368724 discloses a solution of this kind. According to this document, a detection unit receives these radio waves, and wirelessly transmits a tire wear data signal, based on the radio wave signal, to a receiving unit. The transmission of the wear data signal is triggered only when the radio wave signal is above a predetermined level. The driver can then be warned by an alarm device and a display on the receiving unit.
These methods lack precision in their mode of detection and are unreliable, since they are dependent on elements which, being incorporated into the treads, may be degraded over time.
Another approach is that of using the detection of the tire acceleration. Patent document EP 1106397 describes this approach for determining the wear of the tire tread by comparison between a resonance frequency of a radial or lateral acceleration of the tire, deduced by means of a Fourier transform, and at least one stored frequency.
This type of approach is similarly unreliable and imprecise, since it depends on the measurement of acceleration, which is a poor indicator of wear, used in complicated calculations and random comparisons based on stored values.